1. Field of the Invention
The present invention relates to a method of making a mask for patterning a thin film on a substrate, a method of patterning the thin film using the mask, and a method of manufacturing a micro device, which is, for example, a thin film magnetic head, using the methods.
2. Description of the Related Art
For example, micro devices such as thin film magnetic heads or the like which are used for magnetic recording devices are manufactured by patterning a thin film formed on a substrate in a predetermined shape. Specifically, each film is formed using film formation technology such as a plating method, a sputtering method, or the like, patterning technology such as a photolithography method, and removal technology such as etching, a chemical mechanical polishing method, or the like.
For patterning the thin film formed on the substrate, for example, the photolithography method is used. Specifically, a thin film is first coated on a substrate, and a photoresist is coated on the thin film. Then, using a photo mask with a predetermined aperture pattern, the photoresist is exposed in a predetermined pattern. Then, by developing the photoresist, the photoresist in the predetermined pattern is formed on the thin film. Then, by removing a portion of the thin film that is not covered by the photoresist by etching or the like, the thin film can be patterned in the predetermined shape.
In micro devices such as the above-described thin film magnetic heads, there is a demand that a thin film formed on a substrate should be patterned extremely small.
However, in the patterning using the photolithography method, there is a lower limit on the size of narrowing a thin film to be patterned. In other words, due to an optical theoretical limit that is a diffraction limit, there is a limit of narrowing an exposure pattern to the photoresist. Accordingly, only a photoresist pattern with relatively wide width can be formed so that there is a limit of narrowing the thin film that is patterned.
JP Laid-Open Patent Publication No. 2002-116557 discloses a method for manufacturing a resist pattern having even narrower pattern, and a method for narrowing a thin film pattern. Specifically, a milled thin film is formed on a substrate. Then, a polymethylglutarimide (PMGI) layer is coated on the milled thin film. Next, a photoresist layer is coated on the PMGI layer. Then, the photoresist layer is exposed by, for example, ultraviolet (UV) through a mask with a predetermined pattern. Next, a developing treatment to the photoresist layer is performed as well as the PMGI layer exposed from the photoresist layer is removed by alkali solution or the like so that a pre-resist pattern is obtained. Then, an ashing treatment is performed on the pre-resist pattern so that the pre-resist pattern is narrowed.
As described above, by performing the ashing treatment on the pre-resist pattern formed by the photolithography method, a resist pattern that is narrower than the optical theoretical limit can be obtained. By patterning the milled thin film using this resist pattern, even narrower patterning can be performed. Also, a lower portion of the pre-resist pattern, which is the PMGI layer, becomes relatively small by the ashing so that a T-shaped pre-resist pattern is formed.
In Japan Laid-Open Patent Publication No. 2002-116557, a pre-resist pattern is narrowed by an ashing treatment to form a mask, so that the pre-resist pattern is made of an organic material such as PMGI. However, the strength of the organic material is relatively low, and the narrowed mask is more likely to be unstable. As a result, the mask may incline or even fall down. Specially, when making a T-shaped pre-resist pattern, a narrowed mask becomes more unstable.
Normally, it is common that a large number of micro devices are made on a wafer in one time. In the ashing treatment, the degree of narrowing the organic material of the pre-resist pattern by the ashing is more likely to change between a central portion and an outer circumference portion of the wafer. As a result, variation in width of the mask of the narrowed pre-resist pattern occurs, and variations in width and shape of the thin film patterned using this mask may occur.
Therefore, a method of making a mask for further stably patterning a thin film, and a method of patterning using a mask thereof are desired. Such methods can be preferably used for manufacturing micro devices such as thin film magnetic heads.